1. Field of the Invention
The present invention relates to an apparatus for and a method of manufacturing a stack of sheets by feeding the sheets and cutting off corners thereof.
2. Description of the Related Art
X-ray films or the like are produced by cutting a rolled photosensitive medium to successive given lengths as sheets, stacking the sheets, covering the sheets with a protective cover, sealing the sheets in a light-shielding pouch as a packaging material, and shipping the sealed sheets as a packaged product. The shipped packaged product is supplied to an image recording apparatus in which the sheets are delivered one by one by suction cups or the like and images are recorded thereon by a laser beam or the like.
Photosensitive mediums such as X-ray films are coated with an emulsion layer on their surfaces. When the coated surfaces of photosensitive mediums are attracted by the suction cups in the image recording apparatus, the coated surfaces tend to be damaged by the suction cups, possibly causing noise in images that are recorded on the photosensitive mediums. Furthermore, since X-ray films or similar sheets are produced from a roll of elongate film, the produced sheets have a tendency to roll. It is therefore important to take the rolling tendency of the sheets into account when the sheets are manufactured.
In the process of manufacturing sheets, it is necessary to turn them a certain angle in a horizontal plane or invert them, i.e., turn them upside down. However, a stack of many sheets is very heavy and cannot be handled efficiently. Nevertheless, the above operation needs to be performed quickly and reliably.
Furthermore, the stacked sheets that are flexible are required to be fed reliably between various steps of the process of manufacturing sheets.
Japanese laid-open patent publication No. 1-210298 discloses an apparatus in which the central region of the lower surface of a sheet is held by a narrow support having a concave support surface. In the disclosed apparatus, the sheet is curved by the narrow support for increased strength, and is fed in the curved state. The sheet can thus be fed without being flexed from one station to another, and can be transferred easily between the stations.
In the mechanism for feeding a stack of sheets, the delivery of sheets should be made reliably. For example, a stack of sheets needs to be fed without being displaced while being fed. It is desirable to feed sheets while giving certain strength to them regardless of their size, and also to hold and feed stacks of sheets reliably even if different number of sheets are contained in the stacks.
Sheets manufactured as packaged products have their sharp corners cut off into round corners for achieving easy handling and avoiding damage in use.
For example, in the apparatus disclosed in Japanese laid-open patent publication No. 1-210298, a plurality of square sheets are stacked and then aligned at their sides by an aligning unit, and the stacked sheets (hereinafter also referred to as “sheet stack”) are fed to a first cutting unit where two corners are cut off, after which the sheet stack is fed to a second cutting unit where the other two corners are cut off.
In each of the first and second cutting units, the corners of the sheets are simultaneously cut off efficiently. However, while the sheet stack is being fed from the aligning unit to the first cutting unit and from the first cutting unit to the second cutting unit, if the sheets in the sheet stack are displaced out of position, then the following problems tend to arise:
If the sheet stack with the sheets displaced out of position is cut off in the first cutting unit or the second cutting unit, then the severed corners of the sheets may be shaped or positioned differently from each other. Since the two corners are simultaneously cut off in each of the first and second cutting units, these two corners may be shaped or positioned differently if the sheets are displaced out of position.